The compression set of silica-filled rubber largely differs with the amount and type of silica filler, wettability of silica filler with rubber, and other factors. For the purpose of improving the compression set, investigations have heretofore been made on the amount and type of silica filler and a variety of wetters for improving the wettability of silica filler.
Prior art approaches are successful in improving the compression set to some extent, however, better compression sets are required in some applications. There is a desire to have cured rubber having an improved compression set.
The inventors proposed in JP-A 2001-220469, U.S. Pat. No. 6,410,641 and EP 1125973A, which are incorporated herein by reference, a method of treating cured rubber with a hydrolyzable aminosilane or amidosilane having a Si—N bond for thereby producing cured rubber having improved compression set.
This method achieves an improvement in compression set, but requires to use large amounts of hydrolyzable aminosilane or amidosilane. Even when a solvent for swelling rubber is used in combination, large amounts of liquid are necessary. At the end of immersion, the cured rubber has been swollen. In order for the cured rubber to resume the original shape, the swelling liquid must be removed, which needs a cumbersome operation. A further improvement is desired in this respect.